Acoustic device



July 14, 1936.

H. VGERDIEN ET AL ACOUSTIC DEVICE Filed April 5, 1932 O O O O O O O O INVENTOR HANS GERDIEN HANS 0 NM BY Zi M'u-M/ ATI'ORNEY Patented July 14, 1936 UNITED STATES PATENT" oFFlcE ACOUSTIC DEVICE tion I of Germany Application April '5, 1932, Serial No. 603,332

In Germany May 12, 1931 i -5 Claims. (01. live-115.5)

This invention relates to acoustic devices of the electrodynamic type; More particularly it relates to electrodynamic loudspeakers provided with rectangular piston diaphragms having straight conductors.

Whenever large acoustic energies have to be handled with electrodynamic loudspeakers of the type furnished with pistontypediaphragms and straight conductors, it is. found that the diaphragm and the parts associated therewith, especially the current carrying conductors, are subject to non-uniform strains. In fact, itoccasionally happens that the conductors break in the middle. Similar damage occurs also in the diaphragm supporting means.

The difliculty arises as a result of the fact that the diaphragm and the parts pertaining thereto constitute an oscillatory structure or system which, for the usual form of construction, has a natural period of oscillation falling inside or at least close to the frequency range over which vibrations are being transmitted. The elastic component or constituent of this vibratile system resides in the flexibility of the current carrying conductor and also that of the supports. The mass or inertance component consists of the mass of the current-conducting means, the mass of the diaphragm body itself, and the relatively heavy mobile current leads brought to the conductors, the said mobile current-leads in the former forms of construction constituting an essential part of the aggregate mass.

Owing to the undesirable fiexural oscillations of the diaphragm system, in addition to the chances'of damage before mentioned, there is occasioned also an impairment, though slight, of the reproduction of the sounds.

Now, according to this invention, the said difficulties are eliminated by shifting the oscillability of the diaphragm system or else the natural period of vibration of the structure, into a range which lies as far as feasible outside the range of frequency practically to be considered for sound reproduction. With this end in view the following ways and means are suggested, to wit:

(1) The internal damping of the diaphragm system is increased in order to thus diminish the oscillability, this being accomplished particularly by using current-carrying conductors involving high internal friction.

(2) The flexibility of the structure is reduced, for instance, by supplemental stiffening of the diaphragm and by the provision of supporting means consisting of a, readily mobile, non-elastic materialsuch asa fabric or the like.

(3) The oscillating mass of the system is diminished, most particularly by reduction of the mass of the mobile supply leads. r 5,:

Each of the said ways and means is conducive to a diminution of such damages as have in the past been observed, though it is recommendable to have recourse to more than one at the same time. 10

,In the drawing an embodiment of the basic idea of the invention shows, by way of example, a vibratile system with a rectangular corrugated diaphragm and two straight conductors placed parallel to each other. In this system all of the 15 means contributing to a solution are used at the same time.

Fig. 1 shows a plan view of the side of the diaphragm furnished with the current carrying conductors, Fig. 2, a side view intended to illustrate the co-action between the diaphragm and the magnet system of the loudspeaker, Fig. 3 is a section through a conductor, Fig. i is the other side of the diaphragm, and Fig. 5 is a side View looking in the direction of the arrows indi- 25 cated by 5-5 of Fig. 1 to show the connection of a lead to its conductor.

The current carrying conductors 2 attached to the diaphragm l consist of a plurality of layers laid contiguous one to the other, said layers 30 as shown in Fig. 3 being obtained by multiple folding of a laminar body. The folded sheet body is furnished with lateral projections 3 whereby it is secured to the diaphragm, though insulated therefrom. 35

Such a conductor possesses a far higher internal friction than the conductors consisting of a solid bar or rod as formerly used.

The current leads brought to the conductors consist of sheets 4 which substantially extend in 40 the direction of the conductor and parallel tothe plane through the diaphragm. The sheets, similarly as the corrugations of the diaphragm, may also be corrugated. Such current-supply leads are of lower weight than the leads heretofore 45 used which are positioned more or less at right angles to the surface of. the diaphragm.

The supporting means 5, according to this invention, consist of ethyl cellulose or the like or else a fabric impregnated therewith. Such supports combine adequate strength with lower elasticity than the supporting means made of sheet material used in the earlier art.

On the side of. the diaphragm l opposite the conductors 2 there are provided stiifening ribs or fins 6. The latter, like the diaphragm, should most suitably be made of light metal. They may be parallel to one another and be located, for instance, at the same place as the current-carrying conductors, though they could be disposed of wholly or partly diagonally as shown in Fig. 4.

A diaphragm constructed in accordance with the present invention, even in the presence of the highest acoustic oscillations heretofore employed, evidences no tendencies towards a natural period. Also, the breaks often noticed in the past in the current carrying conductors are eliminated.

What we claim is:

1. A vibratile system for electrodynamic acoustic apparatus comprising a rectangular-shaped, piston diaphragm, electrical conductors secured along parallel edges of said diaphragm, and flex-- ible supporting means for said diaphragm secured to the two shorter edges of the diaphragm, each of said conductors consisting solely of a plurality of layers arranged contiguous to each other.

2. In a loudspeaker the combination of a rectangular, piston diaphragm for electro-dynamic loudspeakers, current carrying conductors secured to a face of said diaphragm, corrugations in said diaphragm, said conductors consisting of several contiguous layers, and reinforcing ribs arranged on the corrugated diaphragm on the face opposite the current carrying conductors.

3. In a loudspeaker the combination of a rectangular, piston diaphragm, current carrying conductors secured to a face of the diaphragm, flexible supporting means secured to opposite edges of said diaphragm, said supporting means extending in a direction perpendicularly to the direction of the current carrying conductors, and current carrying leads for the conductors, said current carrying leads consisting of corrugated sheets extending in the direction of the conductors and parallel to the surface of the diaphragm.

4. A vibratile system for an electrodynamic acoustic device comprising an elongated diaphragm, a pair of conductors secured to one side of said diaphragm, flexible supporting means at opposite ends of. the diaphragm and stiffening means on the opposite side of said diaphragm from said conductors.

5. A vibratile system for an electrodynamic acoustic device comprising a rectangular diaphragm, stiffening corrugations in said diaphragm, flexible strips connected along the short sides of said rectangular diaphragm for supporting the diaphragm, a pair of elongated conductors extending along the long sides of said rectangular diaphragm, said conductors comprising a single sheet of material folded to provide a plurality of layers laid contiguous one to the other, and to provide projections extending substantially at right angles to said layers for securing said conductors to said diaphragm, corrugated sheet-like members secured to the ends of said conductors for supplying current to said conductors and stiffening ribs provided on the opposite side of said diaphragm from the side to which said conductors are secured.

HANS GERDIEN. HANS NEUMANN. 

